I truly believe Nasus has the potential to be a tier 1 jungler now
Let me first start by saying how excited I am for the new jungle. For the first time probably ever, if I want to have the maximum potential for success, I don't feel like I am basically required to play Free Win aka Lee Sin (not that I ever played him). For the first time, decision making in the jungle is actually complex from the start. Its not "do I have to gank this lane or this lane after I collect double buffs to match Lee Sin or [insert meta jungler here] in map pressure when I know I likely can't." You have to actually think about routes, you get punished for spending more time attempting to gank and failing and ganking in general is harder now because of the toll the jungle takes on most junglers early (its for this reason I believe counter jungling just got a shit ton harder, too).
So, why Nasus? Well for several reasons but lets look back at made Nasus a tier 1 jungler early season 3. Max E, fast clear. Can solo dragon lvl 6 with ult. Can tax lanes when laners back, constantly keeping lanes shoved. He had utility out the wazoo (still does). At this time, all AD comps were common - level 5 E shreds 45 flat armor. Wither was overpowered as balls, it slowed AS by 95%, eventually getting reduced to 47.5% and rightfully so. His build path was all utility: ancient golem, bulwark, randuins, frozen heart and locket. Obvioisly old locket is no more, bulwark is gone and the juggernaut enchantment is basically ancient golem on steroids.
So why now? Whats so different? Utility Nasus is still decent but wither has been nerfed to hell, league of mobility makes Nasus frown, he doesn't offer hard engage, his ganks are mediocre at best - shouldn't he be tier 3 or below? In the past jungle, absolutely. Not in this jungle though. Innate. Sustain. Actually. Matters. Now. Its harder to gank and do nothing but gank, counterjungling is even harder now, specifically early on and as I noted, Nasus' innate lifesteal lets him stay in the jungle much longer. With LS quints, I was able to clear my 1st entire jungle in one round without recallng - I am under the impression most junglers cannot do that now and he ones who can aren't really huge ganking powerhouses early. Thats a pretty damn big deal.
So what prevented Nasus from being good before? Well, in season 4, the name of the game was pressure. You had to gank. You had to gank a lot. And any weaker early game jungler (like Nasus) was prone to being counter jungled. Nasus couldn't keep up on ganks and he got countered hard by meta junglers because they didn't have to think much - show up at his red, force him to give it up or fight for it (and likely die) and be behind and just accept it. Thats not the case now, Lee can't just show up at your second buff now and level 2 cheese you and if he tries to, hes actually going to be punished for it now if you ward your second buff early and clear other camps while he waits there like a doofus. This alone makes Nasus' life in the jungle much easier. Because after level 4-5, he will fuck anyone up who tries to counter jungle him aside from a few (but those champions are notorious for counterjungling like Udyr for example).
So with that out of the way, what makes nasus good now? Objective control matters and constantly being at high health in your jungle (something nasus has no problem with after upgrading machete) helps a lot. The fact he can solo dragons as easily as he does and as quickly as he does helps a lot - for those who don't know, I will explain why he can. Nasus' ult does 3/4/5% (might be 4/5/6) max health damage in magic damage per burn tic. He then converts that damage into bonus AD, which caps at 250 or 300 iirc (watch a Nasus solo dragon and see his base AD sky rocket while doing dragon). Because of his life steal and flat health gain with ult, dragon alone can't kill him. And he has the tools to burn it down quickly with his ult. So considering this, the name of the game no longer being afk ganking without clearing much (nad Nasus still has decent ganks) and the new jungle favoring him, I think he can be really good in this jungle.
So what are his drawbacks? Well he won't gank early and a concentrated team invade can hold him back but thats harder to execute and with several different potential jungle paths, its hard to predict where he will be to invade him. He doesn't have hard initiation but he has great pick potential. His peel isn't the greatest in league of mobility but you can build to help with both his lack of initiation and weaker peeling.
Before we get into builds, lets address hard intiation - it actually is still really good. Its just tank junglers (who typically bring this) aren't regularly played. The other part is that disengage is even better now. Every meta support shits on initiation: braum, Janna, Nami, Thresh and now Sona. For example, Vi ults a target to start a fight? The following above supports sit between vi and their engaged upon ally and vis team and simply aoe cc the rest of vis team, kill Vi and re-engage. I believe iniation is still good but its not required. And as I noted, itemization can help Nasus with this but keep in mind, iniating under towers now is even harder (but once again, itemization is there for this). But no matter how you slice it, not having hard iniation is a big weakness for jungle Nasus but every jungler has their weakness.
So, itemization. I have been doing 2 early points in E and then Q max for stack farming with aoe push potential, max w last but get a point in it at lvl 3 or 4. I go all utility here but remember CDR is core on Nasus, whether its solo lane or jungle nasus (MANY THANKS TO HYFE FOR DISCOVERING THIS LONG AGO). Iceborn gaunlet gves you more peel, you will probably want that. You want to juggernaut enchantment but don't be afraid of warrior if you're snowballing because it makes you hit like a fucking truck with sheen. Righteous glory is a biggie if you need some hard engage but you will probably want it anyway. Locket is good for added utility and MR (don't be afraid of getting SV though) and discuss ohmrecker and locket with your support. For runes and masteries, i enjoyed LS quints giving me 14.5% LS at level 1 (remember Nasus passive is 10% Ls at lvl 1 then scales to 14% at level 7 and so on). Flat AD quints but I think armor or hybrid pen reds could be good. Flat armor yellows and scaling mr blues (you don't need CDR, your itemization will easily take care of this). You could also do AS or MS quints or even AS reds with MS quints, i haven't tested how this impacts his early sustain yet.
So yeah, sorry for this obnoxiously long post but I am super excited for this and think it can work. I am also diamond so I am a GD overlord or something like that. So feel free to yell at me or give me RP or whatever. And Jatt, if you respond to this, I will give you a dollar.